Chemical reactions in crosslinking of copolymers of ethylene and vinyltrimethoxy silane

The crosslinking reactions of a new type of polyethylene, an ethylene vinyltrimethoxy silane (EVS) copolymer, when reacted with water has been studied. Samples of EVS were treated in water at 90°C. The kinetics of the crosslinking was followed by measuring the gel content and by determination of the content of different structures (SiOCH3,SiOH, and SiOSi) using FT‐IR. The observations show that a maximum gel content of 70‐75% is obtained after 25 h treatment in water at 90°C. On the other hand, the absorption index for the crosslinks, SiOSi, continues to increase until about 100 h, i.e., more crosslinks seem to be formed without a simultaneous increase in gel content. Mechanical measurements showed decreased elongation at break even after very long treatments. Thermo‐oxidative degradation is, however, also responsible for the change in mechanical properties. For properly stabilized samples, the decrease in elongation leveled off after about 100 h of treatment. This indicates that the crosslinks formed after 25 h mainly should be within the already existing gel. The observed synergistic effect of crosslinking and thermo‐oxidative degradation emphasizes the importance of a proper stabilizing system.